1. Field of the Invention
The present invention relates generally to control valves, and more particularly to an axial control valve product that provides high capacity and low noise performance characteristics.
2. Description of the Related Art
As is known in the control valve industry, three well known types of conventional fluid valves include rotary stem valves, sliding stem valves, and sleeve valves. Rotary stem valves generally comprise a rotary shaft or stem which is maintained within a valve body. The rotation of the shaft may be used to facilitate the alignment of a radial port of the shaft with a fluid port of the valve body to open a valve passage. Conversely, the rotation of the shaft may facilitate a misalignment of the ports to effectively close the valve passage. In operation, a typical rotary valve shaft or stem must rotate about 90° relative to the valve body between the fully open and closed positions. There exists in the prior art other types of rotary valve designs which utilize alternative geometries requiring a shaft rotation that is less than 90°, such as three way or angled ball valves.
Rotary valves typically employ the use of seals, and often bearings, which are disposed between the rotary shaft and the valve body to prevent fluid from leaking from the valve body between the shaft and the valve body. In this regard, one of the primary drawbacks of rotary valves is that the significant movement of the shaft typically causes substantial wear to the seals and, if present, the bearings. Thus, the bearings and seals of a rotary valve must typically be replaced over time. Another drawback is that the seals, in order to function properly, also add friction between the valve body and the shaft. Substantial force is therefore typically necessary to overcome the seal friction and rotate the shaft.
A sliding stem valve typically operates on a principle similar to a piston, and includes a valve plug on a stem that slides linearly within a valve body. The valve plug bears against a seat or closes a passage when moved to a closed position, and is spaced from the seat or clears the passage when moved to an open position. The valve stem and the valve plug must usually move relative to the valve body a significant distance between the fully open and closed positions. Like rotary stem valves, sliding stem valves typically employ seals, and often guides, between the stem and the valve body to prevent fluid from leaking from the valve body between the stem and the valve body. In this regard, one of the primary drawbacks of sliding stem valves is that the significant linear movement of the stem causes wear on the seals, thus often necessitating that the seals be replaced over time. Another drawback is that the seals also create friction that must be overcome in order to move the linear stem valve between its open and closed positions.
Sleeve valves typically have a valve body defining an axial fluid flow passage. A stationary valve plug is usually fixed within the valve passage and carries or defines a valve seat positioned on an upstream end of the plug. A slideable valve sleeve is positioned in the valve passage and can be selectively moved between a fully closed position with a downstream end of the sleeve bearing against the valve seat, and a fully opened position with the downstream end of the sleeve being spaced a prescribed distance from the valve seat. Fluid can flow through the valve passage and the sleeve, around the valve plug, and an exit outlet of the valve.
Sleeve valves as known in the prior art typically have a number of prescribed performance characteristics, such as fluid flow rate, fluid pressure, valve flow coefficient, as well as inherent, installed, and linear flow characteristics. Various flow characteristics of sleeve valves can typically be determined or controlled by a number of factors, including the size and shape or contour of the upstream end of the valve plug, the shape of the plug body beyond or downstream of the upstream end, and the passageway or orifice size and contour surrounding the valve plug. Other valve features can be designed and shaped to affect valve flow or performance characteristics as well, including contours of the valve sleeve outlet opening or the like. Along these lines, designing a particular valve plug shape is an often used means to achieve a desired valve performance or flow characteristic. However, as a result, a typical sleeve valve for a given system often has a unique, non-replaceable valve sleeve and plug. Thus, if a different valve flow characteristic is desired for a particular valve or system, or if a valve seat or plug is damaged within a valve or system, it is often necessary to remove and replace the entire valve assembly within the system. In this regard, to change the load characteristics or the valve plug, it has typically been necessary in the prior art to swap the entire sleeve valve with a newer replacement valve.
The axial drag valve constructed in accordance with the present invention is adapted to overcome many of the deficiencies highlighted above in relation to known rotary, sliding stem, and sleeve valve designs. Various novel features of the present invention will be discussed in more detail below.